Tuesday, 1 August 2006

Prevalence and phylogeny of Kakugo virus identified from aggressive worker honeybees (Apis mellifera L.) under various colony conditions

Tomoko Fujiyuki1, Seii Ohka2, Hideaki Takeuchi1, Masato Ono3, Akio Nomoto2, and Takeo Kubo1. (1) Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo, 113-0033, Japan, (2) Department of Microbiology, Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo Bunkyo, Tokyo, 113-0033, Japan, (3) Honeybee Science Research Center, Tamagawa University, 6-1-1 Machida, Tokyo, 194-8610, Japan

We previously identified a novel insect picorna-like virus, termed Kakugo virus (KV), from the brains of aggressive worker honeybees (Apis mellifera L.) that had attacked their natural enemy, a giant hornet (Vespa mandarinia japonica). To examine the relation between KV infection and aggressive worker behavior, we surveyed the prevalence of KV in worker populations engaged in various labors by quantifying KV genomic RNA using quantitative reverse transcription-polymerase chain reaction. KV was detected specifically from aggressive workers in some colonies, while it was detected also from other worker populations in other colonies where the amount of KV detected in the workers was relatively high. This finding suggests that in the primary infection phase KV infection is attacker specific, whereas in the late infection phase KV is infectious to various worker populations. To investigate whether KV strains detected from various worker populations were identical, phylogenetic analysis was performed using sequences corresponding to the RNA-dependent RNA polymerase (RdRp) and virion protein 1 (VP1) regions. There was a less than 2% difference in the RdRp sequences between KV strains from aggressive workers and those from other worker populations, suggesting that all of the viruses detected in our experiments were virtually the same KV. We also found that some of the KV-infected colonies were infested by Varroa mites (Varroa destructor) and sequences of the KV strains detected from the mites were the same as those detected from the workers of the same colonies, suggesting that the mites mediate KV prevalence in the honeybee colonies. KV strains had approximately 6% and 15% sequence differences in the RdRp region from deformed wing virus (DWV) and Varroa destructor virus-1, respectively, and fewer sequence differences with DWV in the VP1 region. These results suggest that KV represents a closely related, but distinct, viral strain from DWV.

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